Electrochemical grinding is a machining process in which two distinct machining actions, in combination, are simultaneously exerted upon an electrically conductive workpiece: the electrolytic dissolution of material from the conductive workpiece produced when a high-density electric current is passed between the workpiece and a tool electrode through an electrolyte that serves as an electrochemical machining medium; and the mechanical abrading of the tool surface against the workpiece. In a finishing operation subsequent to the machining process, only the mechanical action may be utilized using the same tool to give the machined body a shining finish. It is desired therefore that the tool be an electrode body having both good electrical conducting and satisfactory abrading capabilities.
Electrode bodies conventionally used for electrochemically grinding an electrically conductive workpiece consist of a structure of portions functionally divided from one another as regards the conductivity and abrasivity. Thus, typical electrochemical grinding tool electrodes are metal bonded diamond or other abrasive wheels which consist of electrically nonconductive abrasive particles constituting mechanical tools that are supported on and in a metal matrix providing the path for the electrochemical machining current. These bodies are, however, not of sufficient bond strength. Abrasive particles tend to dislodge rather quickly from the metal matrix and therefore the tool body as a whole undergoes considerable wear in the course of a machining operation. In addition, they are comparatively expensive to manufacture and poor in shapability. In another class of conventional electrochemical grinding electrode bodies, a commercially available purely abrasive porous wheel (e.g. vitrified, silicate, rubber, resinoid, shellac or oxychloride bonded abrasive of silicon carbide, boron nitride, boron carbide, aluminum oxide, zirconium oxide, zinc oxide, titanium oxide or diamond) acquires electrical conductivity by having its inner interconnected pores impregnated with conductive materials. The impregnation may be effected with a chemical plating solution so that an electrically conductive coating builds up on the wall portions of the pores by chemical reduction of a metal from the solution. In use of the wheel, the conductive coating provides paths for the electrochemical machining current. The bond between the conductive coating and the abrasive matrix is, however, comparatively poor. Furthermore, the chemically plated coating tends to suffer aging changes and to be oxidized and corroded and the pores tend to be clogged with oxidation and corrosion products in use of the wheel. As a result, the wheel degenerates rather quickly as to both mechanical and electrochemical capabilities.